Passenger elevators generally have a car having a pair of doors and a landing having a pair of hoistway doors. Both the car and hoistway doors open and close approximately in register with each other to allow passengers to enter and exit the elevator car. When the car is not at the landing, the hoistway doors must be locked and in place to protect passengers standing at the landing from entering the elevator hoistway.
It is a safety requirement to equip the hoistway doors with a lock and an electrical contact (or "interlock") to ensure that the doors are positively locked and not missing or lost. A door may be taken off (i.e. missing) for service or due to some accident.
A typical lock consists of a latch attached to a hoistway door and a catch attached to a hoistway header. A typical open electrical circuit interlock consists of a pair of blade springs attached to the catch, and a bridge attached to the latch. If the hoistway doors are closed, the latch engages the catch and bridges the open electrical circuit. The completed electrical circuit sends a signal to a controller which indicates that the doors are locked and it is therefor safe to move the elevator car.
However, when bridge engages the electrical circuit, excessive noise may result. Further, the bridge may bounce away from the electrical circuit, which may lead to maintenance and operation problems.